1. Activity Title: Mitigating Marshes Against Sea Level Rise: Thin-Layer Placement Experiment 2. Focus: Coastal restoration techniques: scientific method, replication, vegetation cover, sea level rise in salt marshes, and thin-layer placement 3. Grade Levels/ Subject: 9th -12th 4. VA Science Standard(s) addressed: BIO.1, BIO.8 c-d, ES.1, ES.8 a, ES.10 a, d-e. Meets objectives for The Virginia Environmental Science Course: I. Scientific Skills and Processes V. Human impact, global climate change, and civic responsibility 5. Learning objectives/outcomes a. Students will explain why the zones of a salt marsh are different b. Students will summarize how sea level rise, erosion, and subsidence affect coastal marshes c. Students will describe the process and goals of thin-layer placement as a restoration strategy d. Students will understand the benefits of the thin-layer placement restoration technique 6. Summary: Students will learn about thin-layer placement restoration techniques by using data from the first year of a plot-based thin-layer restoration science project being conducted by the Chesapeake Bay National Estuarine Research Reserve in Virginia (CBNERR-VA). In groups, students will analyze images of vegetation plots exposed to different treatments and decide which is performing best and could be used as a possible restoration technique to combat sea level rise in the marsh. Students will also interpret graphs of vegetation percent cover, and use classroom discussion to come to a conclusion using critical thinking. 7. Total length of time required for the lesson: 60-90 minutes (may work best if spread between 2 class sessions) 8. Key words/Vocabulary: Accretion Beneficial Reuse Biochar Community Structure Control Dredging Ecosystem Services Erosion Estuary Inundation Reference Plot Resilience Restoration Subsidence Thin-Layer Placement 9. Background information Marshes are a type of wetland dominated by grasses that are frequently flooded with water, a process called inundation. Marshes provide a variety of ecosystem services for humans including buffering wave energy to protect coastlines, trapping sediments and filtering runoff to improve water quality, reducing impacts of flooding, and providing recreational opportunities. In addition, these habitats are important for many fish (especially as nursery areas) and wildlife (Barbier et al., 2011). Since marshes are a transition area between land and sea, they vary in properties such as salinity, water level, temperature and oxygen, as you move inland from the shoreline. Marsh zonation is heavily influenced by the frequency and duration of flooding. The zones can be thought of as four different parts: “low marsh”, with regular flooding by high tide, “salt meadow” with periodic flooding during extremely high tides, “salt panne” with infrequent flooding, and the “upland bank”, with flooding only during extreme weather events or irregular conditions. This zonation is visible by the different dominant species of vegetation in each zone that are adapted to grow there (Chesapeake Bay Program, 2004) (CCRM, 2019). The zones in a salt marsh are maintained by physical interactions with the tides, salinity, and extreme weather events or flooding. In addition, competition between species keeps them in their respective zones. When moving from the shore to the high marsh zone, vegetation species change in abundance and dominance. Few species are adapted to lower elevations, like Smooth cordgrass (Spartina alterniflora), which dominates the low marsh area, which has high salinity and is flooded often. In higher elevations, there is less flooding and salinity, which allows species such as Saltmeadow cordgrass (Spartina patens) and Salt grass (Distichlis spicata) to dominant in a mixed marsh species community structure (Bertness, 1991; Morris, Sundareshwar, Nietch, Kjerfve, & Cahoon, 2002; Chesapeake Bay Program, 2004; Perry and Atkinson, 2009). Global sea level rise (SLR) is affecting many coastlines, including the areas surrounding the Chesapeake Bay estuary (Morris et al., 2002; VIMS, 2018). In addition, subsidence, sinking of the ground, is a major factor contributing to local sea level rise which varies throughout the Bay. Subsidence could be caused by a combination of the retreat of glaciers from the previous ice age, sediment loading adding too much weight on the wetlands, and sediment compaction after groundwater removal (Eggleston & Pope, 2013). Erosion is also occurring on the shoreline, causing loss of the marsh land on the coast. Salt marshes are able to migrate towards the forests and further inland to try and survive, but they may not be able to keep up with the rate of SLR (Kirwan, Walters, Reay, & Carr, 2016). In response to sea level rise, marshes have two mechanisms: 1) vertical accretion and 2) horizontal migration. Some marshes are able to build vertically by accumulating sediments and organic matter. This vertical development is referred to as accretion. Secondly, some marshes can migrate horizontally away from the shoreline into higher elevations. For example, as flooding becomes more frequent and gets more intense, the high marsh species drown and cannot withstand the rising water level and salinity. High marsh species die and the lower marsh species begin to take over that space (Raposa, Weber, Ekberg, & Ferguson, 2015; Kirwan et al., 2016). This can cause a narrowing of the high marsh and potential loss of some intertidal habitat (Pontee, 2013). In addition, some marshes cannot migrate if there are barriers such as roads, houses, rocky cliffs, or any kind of shoreline armor (The Nature Conservancy & NOAA, 2011). If the rate of SLR is too high, marshes or grass species will not be able to migrate or accrete fast enough to maintain elevation, and will drown (Weis & Butler, 2009). Scientists are trying to improve the ability of marshes to withstand change, known as their resilience, by increasing marsh elevation for maximum vegetation growth and to keep marshes from eroding away. To do this, a relatively new restoration strategy being tested and/or implemented in many places to enhance marsh resilience is thin-layer placement (TLP). TLP can be defined by the US Army Corps of Engineers as “purposeful placement of thin layers of sediment (e.g., dredged material) in an environmentally acceptable manner to achieve a target elevation or thickness. Thin-layer placement projects may include efforts to support infrastructure and/or create, maintain, enhance, or restore ecological function” (Berkowitz, Welp, Piercy, & Vanzomeren, 2019, p. 6). The goal of TLP is to maintain marsh communities in their position relative to sea level rise. In addition, this strategy has the potential to be a “win-win” situation if the sediment placed on the marsh surface is from local dredging, giving dredging sediments the opportunity for beneficial reuse. However, since this is a novel approach, more research is needed to evaluate the effectiveness across diverse conditions and to standardize a national framework for TLP and monitoring protocols (Raposa, West, Wasson, Woolfolk, Endris, & Fountain, 2017). Researchers have begun evaluating different strategies and treatments for TLP across the nation. The National Estuarine Research Reserve (NERR) System Science Collaborative funded a two- year experiment at 8 different NERR sites to provide broad geographic scale, including the Chesapeake Bay NERR in Virginia (Raposa et al., 2017). The three core research questions about TLP they are trying to answer include: “Is sediment addition an effective adaptation strategy for marshes in the face of sea level rise? How does marsh resilience respond to different levels of sediment addition? How do low versus high marsh habitats differ in their response to this restoration strategy?” (Raposa et al., 2017). Each reserve site also will be answering secondary questions, such as determining how the use of biochar, which is carbon rich material, or the use of a local dredged sediment sources affects plant growth and nutrition. At CBNERR-VA, for example, the study design includes an extra treatment using local dredge material from a recent shoreline enhancement project (Raposa et al., 2017). The experiment is looking at three factors for change: marsh elevation, vegetation cover, and sediment properties. Each reserve has established locations in both the high marsh and low marsh habitats to test how different sediment thicknesses affect vegetation. At each reserve, there are five sites in the high marsh and five in the low marsh. In both the low and high marsh habitats, there are treatment plots enclosed by a 0.7 m x 0.7 m wooden frame in order to reduce sediment slumping, erosion, and loss. All reserves have between 40-50 treatment plots total. All sites include one control plot with no frame, one control plot with a frame, one plot with a thin standard sediment treatment, and one plot with a thick standard sediment treatment. The control plot tests the effects of the frame and site selection because it does not receive treatment. One reference plot is chosen 10 to 20 centimeters higher in elevation than the treatment plots and represents the restoration goal. A standard composition of mud and sand is used as the sediment source in all reserves (Raposa et al., 2017). At the NERRs in Chesapeake Bay, Virginia, North Carolina, and San Francisco Bay, there is an additional treatment plot within each site with 14 cm of local dredged material. At the NERRS in Elkhorn Slough, Caliornia, Narraganesett Bay, Rhode Island, and Waquoit Bay, Massachusetts, there is an additional treatment plot within each site with 14 cm treatment with biochar added. Researchers at the reserves monitor changes in marsh vegetation, elevation, and sediment properties in these plots over the two years to capture two growing seasons. The results in this lesson are not conclusive; instead, scientists are still experimenting on which treatment is best and if this will work in all areas. However, this is an example of experimenting before restoration, or a controlled, small scale experiment. It will be useful for comparison to larger scale experiments and will supplement research in the field of thin-layer placement.